Rapid prototyping includes many techniques used to produce 3-D objects from computer data representing the 3-D objects. The 3-D data may be referred to as Computer Object Data (COD); other 3-D data may be used. Some specific formats of COD data which may be used are STL data and CAD data; other formats may be used. A common example of COD is Computer Aided Design (CAD) data. The machine's controller converts the data to the form as required by the object building components of the machine. Most of the RP techniques use fluid or fluid-like interface material, which is solidified to produce the solid object. The interface material is usually referred to as build material (BM) or model material. Building the object is usually performed by producing thin layers corresponding to the data and solidifying the layers one upon the other. Solidifying the layers may be achieved in different ways, such as by cooling the layers, in case of using molten wax-like materials, by exposing the BM to electromagnetic irradiation of appropriate wave-length, in case of using a photopolymer as BM, or other methods, such as chemical curing.
Various systems for computerized 3-D printing have been developed. For example a system from 3-D Systems, Inc. of California USA operates on the basis of stereolithography (SL) where a focused ultraviolet laser is scanned over the top of a bath of photopolymerizable liquid polymer material. Specified sections of the surface of the bath are polymerized or cured by contact with the UV laser beam creating a solid plastic layer at or just below the surface of the material. The beam location and thus curing location may be controlled by a printer controller or computer. One method of stereolithography is described in U.S. Pat. No. 6,126,884 issued Oct. 3, 2000 to Kerekes et al. Another technique for building a 3-D model in layers is described by Cima et al., U.S. Pat. No. 5,387,380. A layer of powdered material is deposited followed by the deposit of binding material in selected parts of the powder deposit to form a layer of bound powder in these parts. These steps are repeated for successive layers to form a desired component.
In one technique, the controller of the printer receives, for example, COD data and converts it to the format applicable for the printing process (for example, sliced COD data). The technique is typically based on dispensing typically two materials (other numbers may be used) from, typically, ink-jet heads. The materials are, for example, BM and support material (SM). The BM is dispensed at those locations the object is to be built. The SM is dispensed at other places, provided it is needed there. The BM and SM are typically dispensed simultaneously according to the computer data.
The BM may be a specially formulated photopolymer, which is typically cured by a source of electromagnetic irradiation, for example a flood or wide area of light, which is usually UV, but other wavelengths may be used. The SM is also typically a photopolymer, which is used to support the BM prior to, during and/or after building. The SM is so formulated as to be easily disposed of or removed at the conclusion of the object building process.
The size of the object actually built may differ from the size of the prototype model desired to be built, or from the size as defined by the input data. Even if the inaccuracy is minimal, the error may have serious consequences when, for example, two or more pieces are meant to fit together, and a minor difference in size may render a close, exact fit impossible. An accuracy of, for example, ±0.2 mm may be acceptable in the art of 3-D printing. Larger inaccuracies are less acceptable.
Such inaccuracies may result from various factors, such as material shrinkage or inaccuracies in leveling layers of material. Various other aspects of 3-D printing may reduce quality of printed objects. If more than one material is used, materials may diffuse into each other. Materials may alter their shape after deposition due to, for example, thermal contraction, the tendency of materials to merge, or the chemical reaction of the interface materials to curing. Materials may not be deposited accurately due to, for example, defective or missing print head nozzles or the velocity of the print head. Other factors may cause object creation inaccuracies.
Therefore, there is a need for a device, system and method that reduces inaccuracies in three dimensional printing.